@Maciamo,
*Relatively* speaking the Myceneans were mixed. All of their ancestors don't have to have lived in Greece for 20,000 years for them to be unmixed. The genetic shifts we see in ancient DNA; EEF migration, Steppe migration, occur once every like 5,000 years. For the most part people were born, had kids, and died on the same plot of land.
Mycenaeans were by and large EEF. The models give them like 70% EEF. Some EEF would have come from the north alongside Steppe admixture, some came alongside CHG admixture, but still by and large Myceneans traced their ancestry back to the Neolithic Aegean or at least Neolithic Greece and Turkey.
European genetic diversity is more complex than EEF, WHG, CHG, EHG. The EEF's in Poland may be more related to Sardinians than to Eastern Europeans but they share unique genetic markers (eg, mtDNA H1b2) only with Eastern Europeans. While there are other Europeans with a more similar EEF/EHG/etc. composition to Myceneans than what modern Greeks have, modern Greeks probably have the closest genealogical relationship with Myceneans.